The mechanism of action, the regulation and the roles in intermediary metabolism of the enzymes involved in the conversion of thymidine to the pyrimidine nucleosides of RNA are being studied in Neurospora crassa, Rhodotorula glutinis and mammals. The enzymes which are being purified and subjected to mechanistic studies include those that catalyze the reactions of the following pathway: Pyrimidine deoxyribonucleoside yields Ribonucleoside yields Pyrimidine plus Ribose Thymine yields 5-Hydroxymethyluracil yields 5-Formyluracil yields Uracil-5-carboxylic acid yields Uracil plus CO2. The studies involving the alpha-ketoglutarate dioxygenase reactions are being emphasized.